This invention relates to a process for producing fine copper powder with enhanced sinterability. More particularly, the proces involves fluid energy milling dendritic copper powder to produce cold-worked powders. The particle size is reduced and the copper particles are equiaxed in shape.
Replacement of precious metal powder by copper powder for thick film paste hybrid circuit applications is a current trend in the electronic circuit fabrication industry. Copper offers several economic and performance advantages over precious metals. However, copper thick film paste technology is in its infancy, and many improvements still must be made in the process. One of these improvements is enhancing the sintering characteristics of the copper powder.
Cold working the powder before sintering enhances the sinterability of the powder. Strain energy is stored in the powder in the form of dislocation tangles, etc. The energy is released during sintering and allows the use of lower sintering temperatures. Lower sintering temperatures lead to lower furnace energy costs and usually less capital investment in sintering furnaces as well as potential for greater flexibility in the selection of associated thick film paste materials. Typically the powder is ball milled to a fine "flaky" morphology having a diameter to thickness ratio of &gt;about 10, prior to sintering. However, this is not usually desirable for thick film paste feedstock, since an equiaxed geometry is preferred to enhance packing density of the powder.